UNION COUNTY, NJ — Residents who found the recent tropical heat wave stressful should imagine what the hot weather did to the trees.

That’s the message from Union County arborist Bob O’Rourke, who suggests giving local trees some love during the summer. An arborist for more than 20 years who has been in the tree-trimming industry for more than 30 years, O’Rourke recommends helping trees proactively, not reactively.

“While heat doesn’t usually kill a tree on its own, it can lead to it when combined with disease and/or boring insects,” said O’Rourke, the district manager for Davey Tree Expert Company’s New Jersey office. “That said, younger trees between one and two years old can die from heat alone.”

O’Rourke, who spoke to LocalSource by phone on July 24, made his plea following the weeklong period from July 16 to 22, when temperatures climbed above 95 degrees for five of six days. The heat reached a peak of 99 degrees on July 21 at Newark Liberty International Airport before storms rolled through the area the following day causing the thermometer to plunge more than 20 degrees.

As August is usually the hottest month of the summer, it’s important to know what steps to take to help prevent long-term damage to trees, O’Rourke said. It is important to know that trees feed themselves in a cycle. They pull water from the ground to their leaves, where chlorophyll — their food — is produced. When the stress of extreme heat is introduced, this cycle is slowed. Larger trees such as oak go into a form of dormancy when exposed to intense heat, so they are weakened less than smaller trees, he said.

Heat isn’t as damaging if rain occurs every two to two-and-a-half weeks, but if a dry period extends into a third week, damage starts to occur. The first step to take in preventing heat damage to our trees, O’Rourke said, is to water them once a week before a drought. Doing this will help nurture their food cycle and prevent it from slowing.

If the drought is severe, it is a good idea to fertilize the trees in September, which helps the tree get off on the right foot the following year.

To identify heat-damaged trees, the best place to look is at their leaves. As severe heat starts to take its toll on trees, the outer ridges of their leaves tend to burn. Visible browning on the outer areas of the leaves indicate that the tree is not getting enough moisture. In some cases, the leaves can even start to curl.

Dead trees can lead to what arborists call “zombie trees,” which appear healthy but have defects, and they can eventually lose limbs or topple over during storms or heavy snowfall. And winter is coming.